DOMParser is not defined at defaultParseHtml

Good news - this is a common issue with a straightforward solution! The DOMParser is not defined error occurs because @sanity/block-tools relies on browser APIs like DOMParser to parse HTML, but when you're running code in Node.js (which is what sanity exec does), these browser APIs don't exist.

The fix is to provide a custom parseHtml function that uses a Node.js-compatible DOM parser like jsdom. Here's how to do it:

1. Install jsdom:

npm install jsdom

2. Provide a custom parseHtml function:

When you call htmlToBlocks, you need to pass a parseHtml option that uses jsdom instead of the browser's DOMParser:

import {htmlToBlocks} from '@sanity/block-tools'
import {JSDOM} from 'jsdom'

const blockContentType = // your schema type definition

const html = '<p>Your HTML content here</p>'

const blocks = htmlToBlocks(html, blockContentType, {
  parseHtml: (htmlString) => new JSDOM(htmlString).window.document
})

The key is the parseHtml option - it tells @sanity/block-tools to use jsdom's DOM implementation instead of expecting a browser environment.

Why this happens:

The README example shows the basic usage, but doesn't explicitly mention that you need jsdom for Node.js environments. The defaultParseHtml function in the package (the one throwing your error at helpers.js:173:35) assumes it's running in a browser where DOMParser is globally available.

As mentioned in Sanity's migration course, this is a standard setup when using @sanity/block-tools in Node.js contexts like scripts, migrations, or sanity exec commands. The package is designed to work in both browser and Node.js environments, but you need to provide the DOM polyfill for Node.js yourself.